The role of chromosomal proteins in maintaining the structure and regulating the function of chromatin is studied. Antibodies against histones and non-histone chromosomal proteins have been elicited. Part of the antibodies to protein HMG-1 are directed against sequential determinants. Antibodies to the globular region of the differentiation-related protein H1 degree have been elicited and characterized. Functional antibody and antibody fragments have been microinjected into the nuclei of oocytes from Pleurodeles and into the cytoplasm and nuclei of human KD fibroblasts. The intact IgC cannot transverse the nuclear membrane, but the F(ab)2 fragment can. Microinjection of control IgG molecules did not inhibit transcription. In contrast, microinjection of affinity-purified antibodies to HMG-17, histone H2A and H3 did inhibit transcription. The monovalent Fab fragment also inhibited transcription, suggesting that these proteins are present along the transcribable DNA.